Subunit vaccines are considered safe, but are relatively ineffective in comparison to live attenuated virus vaccines. For HIV-1, the use of a live attenuated vaccine is controversial and additional studies are necessary to determine the feasibility of its implementation. The alternative approach, vaccine trials using viral proteins, has been carried out; however, the results are disappointing as some vaccinees in the trial succumbed to infection. Multiple factors may contribute to the failure of these vaccines; among them, a weak humoral immune response and almost undetectable cellular immunity. The aim of this proposal is to significantly enhance these immune responses by modifying the viral subunit vaccines. To significantly enhance the humoral immunity, we will modify the HIV-2 recombinant envelope glycoprotein, gp105 with an alpha-galactosyl epitope (a-Gal), strongly recognized by endogenous antibodies in humans and old-world primates. The modified protein, complexed with the anti-a-Gal antibody is expected to increase their uptake by antigen presenting cells and thus increase humoral immune responses to gp105. Secondly, to increase cell-mediated immunity, we will express a fusion protein of gag p55 with the tat transfer peptide (TTP). Attachment of this peptide to proteins allows their internalization, localization and processing by cells. When internalized and processed by cells bearing the major histocompatibility class I molecule, selected epitopes will be displayed, thus stimulating the specific proliferation of cytotoxic T-cells. These two modified proteins constitute the key elements of a novel formulation for a subunit vaccine to prevent the infection of Macaca nemestrina with the pathogenic strain HIV-2 287. The protective effects of this formulation will be compared to those conferred by the unmodified proteins by measuring markers associated with disease progression, such as CD4+ lymphocyte numbers, viral loads, and AIDS associated symptoms. Factors associated with immune protection will be evaluated by measuring total and neutralizing antibodies, and delayed type hypersensitivity responses to address the induction of cell mediated immunity against vaccinated macaques. The results from this pilot study will be important for the design of new vaccines against HIV-1, and to gain critical information on the immune responses important for protection.